Here is a simple circuit of an FM booster that can be used to listen to programmes from distant FM stations clearly. This amplifier will pull in all distant FM stations clearly. The circuit is configured as a common-emitter tuned RF pre-amplifier wired around VHF/UHF transistor Q1.
2SC2570. (Only C2570 is annotated on the transistor body.) Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/ output trimmers (VC1/VC2) for maximum gain.
All capacitors are ceramic and 50V is the standard but the 25V types work fine too. Trimmer capacitors Tr1 and Tr2 (22pF) are adjusted for maximum gain. Input coil L1 consists of 4 turns of 20SWG enamelled copper wire over a 5mm diameter former. It is tapped at the first turn from the ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration is shown in the diagram.
2SC2570. (Only C2570 is annotated on the transistor body.) Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/ output trimmers (VC1/VC2) for maximum gain.
All capacitors are ceramic and 50V is the standard but the 25V types work fine too. Trimmer capacitors Tr1 and Tr2 (22pF) are adjusted for maximum gain. Input coil L1 consists of 4 turns of 20SWG enamelled copper wire over a 5mm diameter former. It is tapped at the first turn from the ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration is shown in the diagram.
Component List:
- R1 = 27K
- R2 = 270 ohm
- R3 = 1K
- Tr1,Tr2 = 22pF, trimmer cap (15-40pF)
- C1,C2 = 5.6pF
- C3 = 0.001uF (1nF), ceramic
- C4,C5 = 10pF, ceramic
- C6 = 0.1uF (100nF), ceramic
- Q1 = 2SC2498, 2SC2570, 2N5179, SK9139, or NTE10. NPN VHF/UHF transistor
- L1 = 4 turns of 20SWG magnet wire, 5mm diameter. (so-called 3T+1)
- L2 = 3 turns of 20SWG magnet wire, 5mm diameter.
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